Electrodeposition coating processes have been a widely used for applying anti-corrosive primer coatings to various metallic substrates such as automobile bodies because they are applicable to a variety of substrates regardless of shape or configuration and also hazardless to attendant workers and to the environment. Coating compositions used in the electrodeposition processes are in the form of an aqueous solution or dispersion of electrically charged resin particles. Accordingly, their stability and throwing power are important for the consistent operation of an electrodeposition coating line. With regard to finished coating films, it is desirable to have a large film thickness and high performance properties in such a field as automobile painting where a high corrosion and chipping resistance is essential. Furthermore, there is ever growing needs among users for coated articles having a highly aesthetic appearance in terms of sharpness and gloss.
It is known that the throwing power of an electrodeposition coating composition may be improved by incorporating thereto an amount of pigment particles having a suitable particle size. Japanese Laid Open patent application 58-47067 discloses the addition of resinous components used in a pulverulent coating composition into electrodeposition coating compositions to improve the throwing power thereof. Japanese Laid Open patent application 55-135180 proposes to incorporate an emulsion of polymers having a functional group capable of crosslinking with a base polymer in order to improve the throwing power of the electrodeposition coating composition containing said base polymer. Japanese Laid Open patent applications 55-49766 and 58-93762 disclose an electrodeposition coating composition containing crosslinked polymer particles or powder for use in giving a mat finish on a glaring surface such as aluminum or aluminum alloy substrates.
These known compositions containing pigment or resin particles suffer from certain disadvantages in that they are not so effective as desirable in enhancing the throwing power, that other properties such as storage stability or film appearance are adversely affected, and that they are not adapted for a wide variety of uses.